Coherent modulation formats are of primary interest for long-haul and metro applications, and are gaining increased attention for shorter-reach and data center interconnect (DCI) applications. However, coherent modulators in silicon are inherently high-loss due to modulating both phase and amplitude. For upcoming 600GB, 800GB, and 1TB applications, the transmitter insertion loss of the coherent modulators is estimated at 25-29 dB. Meanwhile, the required transmitter output power into the optical fiber is between 0 and +3 dBm. To meet this requirement, an Integrated Tunable Laser Assembly (ITLA) would need to achieve +25 to 30 dBm output, or up to 1 Watt. Such a laser is prohibitive from both a cost and power consumption point of view. Currently, tunable lasers are only available with +18 dBm output power.
An inline amplifier (e.g., micro Erbium-doped fiber amplifier (EDFA)) can be used to relax the required input power from the laser. However, adding the inline amplifier introduces excess noise into the modulated signal, which can significantly reduce transmission distance. As modulation format complexity increases, higher output optical signal to noise ratio (OSNR) is desired. For 1TB optical links, greater than 45 dB OSNR is desired. Thus, no more than 3-4 dB of gain is achievable due to noise introduced by the inline amplifier.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.